This invention relates to methods for measuring particulate matter in gas, such as for environmental sampling.
Epidemiological studies in the U.S.A. and abroad have shown associations between mortality and morbidity and human exposure to ambient particulate matter (Schartz and Dockery, Am. Rev. Resp. Dis. 145:600, 1992; Pope et al., Am. Rev. Resp. Dis. 144:668, 1992). To date, there is limited knowledge about physical or chemical properties of particulate matter that are responsible for these health effects and there is an increasing interest in developing accurate measurements in the near future.
These associations have been initially demonstrated for total suspended particulates (TSP) and particulate matter (PM) with a diameter of  less than 10 xcexcm (PM10); however, results from other studies suggest that fine particles (PM2.5) and particle components, such as sulfate (SO42xe2x88x92), and aerosols with strong acidity (H+), also may be associated with increased mortality and other adverse health impacts (Ayres et al., Environ. Health Persp. 79:83-88, 1989; Bates and Sizto, Environ. Health Persp. 79(1):69-72, 1989; Bates et al., Environ. Res. 51(1):51-70, 1990; Dockery et al., Am. Rev. Resp. Dis. 147(4):A633, 1993; Raizenne et al., Am. Rev. Resp. Dis. 147(4):A635, 1993; Raizenne et al., Environ. Health Persp. 79:179-185, 1989; Thurston et al., J. Expos. Anal. Environ. Epid. 2(4):429-450, 1992; and Thurston et al., Amer. Rev. Resp. Dis. 147(4):A633, 1993).
The U.S. EPA has recently recognized the need to develop continuous measurement techniques for inhalable particulate matter (PM10 and PM2.5). Results from several studies have begun to expand our knowledge about the relationship between outdoor, indoor, and personal levels of PM10 and PM2.5, and sub-components thereof such as SO42xe2x88x92 and H+. Outdoor studies conducted to date (Lioy et al., J. of the Air Poll. Cont. Assoc. 38:668-670, 1988; Suh et al. J. of Expos. Anal. And Environ. Epid. 4:1, 1994; Jones et al., Atmosph. Environ., 2000) have provided convincing evidence that outdoor PM10, PM2.5, and SO42xe2x88x92 concentrations are quite uniform within both rural and urban communities. The same studies have also shown that outdoor H+ concentrations do not vary spatially within rural communities, but may exhibit substantial spatial variation within urban environments. From studies of indoor environments, it is clear that significant fractions (50-90%) of outdoor PM10, PM2.5, SO42xe2x88x92, and H+ penetrate indoors (Thomas et al., J. Exp. Anal. And Environ. Epid. 3(2):203-226, 1993; Wallace, J. of the Air and Waste Manag. Assoc. 46(2):98-126, 1996; Abt et al., Environ. Sci. and Tech., 2000). Once indoors, these particulate species may be deleted through deposition onto surfaces, or in the case of H+, through reaction with other pollutants present indoors. Indoor particulate concentrations are further affected by the myriad of indoor sources, which include cooking, resuspension, and smoking. As a result of these sources, indoor particulate concentrations are often higher than corresponding outdoor levels. These findings, in conjunction with the fact that people spend the majority of their time indoors, suggest indoor sources to be important contributors to personal exposures to PM10 and PM2.5.
Several studies have found both indoor and outdoor concentrations to be poor estimators of personal exposures to PM10 and its components, as neither indoor nor outdoor concentrations suffice to account for the observed interpersonal variability in their exposures. Daytime personal PM10 exposures were found to be approximately 50% higher than corresponding indoor and outdoor levels (Thomas et al., J. Exp. Anal. And Envrion. Epid., 3(2), 203-226, 1993), while personal SO42xe2x88x92 and H+ exposures were found to be higher than indoor, but lower than outdoor concentrations (Suh et al., supra). The concentration of a pollutant varies from location to location; therefore concentration values obtained by stationary monitors may not be representative of human exposures to particulate pollutants. Furthermore, a person""s activities can alter the patterns of exposure to contaminants throughout the day.
In order to accurately assess individual exposures to ambient particles it becomes necessary to use personal monitors. Nevertheless, the development of reliable personal particle monitors has been impeded by several technical challenges. The smaller sampling pump size, the reduced volume or surface of the collection medium and finally the fact that the energy source required for the device is from a self-contained source, all limit the amount that can be collected within a time period (Clayton et al., J. Exp. Anal. And Environ. Epid., 3(2):227-250, 1993; Morandi et al., Environ. Monitor. And Assess. 10(2):105-122, 1988; Spengler et al., Environ. Sci. and Technol. 19:700-707, 1985). In addition, existing personal monitoring devices provide very little information in the PM size distribution (at best they measure PM concentration below 2.5 xcexcm). Information obtained from more accurate personal monitoring devices that are user-friendly and inexpensive will allow large populations to be studied, thereby providing the much-needed data on the relationship between outdoor and indoor concentrations and personal exposures as a function of particle size and chemical compositions.
The invention provides a personal sampler for PM that allows separation of airborne particles in several size ranges and operates at a high flow rate (9 L/min) by personal sampling standards that makes chemical analysis of the size-fractionated particles possible within a period of 24 hours or less.
The invention provides a personal cascade impactor sampler (PCIS), comprising a miniaturized cascade impactor. The miniaturized cascade impactor comprises four impactor stages followed by an after-filter. The PCIS operates at a flow rate of about 9 liters per minute and has a pressure drop of about 11 in H2O.
The invention provides a device comprising an inlet port at a first end; a plurality of orifice plates, each orifice plate comprising an orifice; a plurality of impactor stage plates, each impactor stage plate comprising an impaction surface having a predetermined cutpoint for particulate matter; and a filter plate at a second end, wherein the inlet port is fluidly connected to the filter plate such that a pressure drop from the first end to the second end is between about 8 and 15 inches of H2O, each orifice plate and impactor stage plate alternately disposed between the first end and second end, wherein each orifice plate is immediately followed by an impactor stage plate.
The invention further provides a personal cascade impactor sampler (PCIS) system. The PCIS comprises a miniaturized cascade impactor assembly (MCIA) having an inlet port at a first end; a plurality of orifice plates, each orifice plate having an orifice; a plurality of impactor stage plates, each impactor stage plate comprising an impaction surface having a predetermined cutpoint for particulate matter; and a filter plate at a second end, wherein the inlet port is fluidly connected to the filter plate such that a pressure drop from the first end to the second end is between about 8 and 15 inches of H2O, each orifice plate and impactor stage plate alternately disposed between the first end and second end, wherein each orifice plate is immediately followed by an impactor stage plate. The PCIS system also comprises a pump, fluidly connected to the MCIA and a power device such as, for example, a lithium battery pack in electrical communication with the pump.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.